The present invention relates to an inspection method of detecting defects of a pattern to be inspected and an apparatus therefor, and more particularly to a method and an apparatus for inspecting a thin film transistor liquid crystal substrate used for a liquid crystal display apparatus, as a pattern to be inspected.
FIG. 1 shows an example of an electric wiring construction of a thin film transistor active matrix substrate (hereinafter referred to simply as "thin film transistor liquid crystal substrate") in the case of arrangement in 5.times.5 pixels. As seen from this, the thin film transistor liquid crystal comprises scan lines 11-15 and signal lines 21-25, and intersections between the signal lines and the scan lines are provided with a thin film transistor 7 and a transparent pixel electrode 8 formed on a glass substrate. When the thin film transistor liquid crystal substrate and a common electrode substrate are opposed in parallel to each other, a liquid crystal display apparatus is basically constructed by enclosing a liquid crystal between both substrates. In FIG. 1, numerals 11p-15p designates electrode terminal pads corresponding to the scan lines 11-15, and numerals 21p-25p designate electrode terminal pads corresponding to the signal lines 21-25.
In the thin film transistor liquid crystal substrate constructed as above described, if a short circuit defect 3 is produced between the scan line 13 and the signal line 23 for example, the display failure along the scan line 13 and the signal line 23 is produced linearly. The short circuit defect 3 includes a short circuit defect 3a which occurs at an intersection point between the scan line and the signal line and a short circuit defect 3b which occurs within the thin film transistor 7 as shown in FIG. 2(a). As measure for correcting these short circuit defects 3a and 3b, a method of providing the intersection between the signal line and the scan line and the thin film transistor 7 plurally has been considered as shown in FIG. 2(b). According to this method, the wiring is cut at wiring cutting positions 9a, 9b such that the short circuit defects 3a, 3b can be corrected. When this method is actually applied, however, the position of the short circuit defect must be previously specified.
FIG. 3 shows an inspection method in the prior art confirming whether a short circuit defect exists or not. According to this inspection method, one end of each of the scan lines 11-15 is connected in common through scan line electrode terminal pads 11p-15p, external wirings 11d-15d, and a connection wiring 1c, and on the other hand, one end of each of the signal lines 21-25 is connected in common through signal line electrode terminal pads 21p-25p, external wirings 21d-25d, and a connection wiring 2c. In such a connection state, if probes are contacted with the connection wirings 1c, 2c, and a voltage V is applied between the scan lines 11-15 and the signal lines 21-25, and a current value is measured by a current meter 4, a decision can be effected regarding whether a short circuit defect exists or not. According to this method, however, even if it can be confirmed that a short circuit defect exists, the pixel address of the short circuit defect producing pixel cannot be specified.
In order to specify the pixel address, when the thin film transistor liquid crystal substrate having the wiring structure shown in FIG. 1 is used as an object, measurement of a current value in the state of applying the voltage V only to one scan line and one signal line at a time may be carried out for all of the combinations of the scan lines and the signal lines in sequence. According to this method, however, since the current value must the number of signal lines, in order to specify the pixel address of the short circuit defect producing pixel, not only is the current measuring work troublesome but also much time is required.
In addition to such disadvantages, damage of an electrode terminal part due to contact of a probe becomes a problem. In order to reduce the inspection time, many probes may be contacted simultaneously such that the pixel address of the short circuit defect producing pixel can be quickly specified. However, in the thin film transistor liquid crystal substrate where the intersection between the scan line and the signal line and the thin film transistor are provided plurally as shown in FIG. 2(b), it cannot be specified at which intersection between the scan line and the signal line or at which thin film transistor a short circuit defect exists.
The inspection time, Japanese patent application laid-open No. 1-154092 discloses a method of detecting defects from a coloring state of a color film of an electrochromic display panel. According to this, since the color film is in a non-coloring state or a coloring state depending on the conduction state of each pixel electrode, the defective pixel can be specified. However, according to this method, since the pixel electrode of the thin film transistor liquid crystal substrate and the color film of the electrochromic display panel must be conduction-connected through an electrolyte, a problem of contamination remains in the case of using a liquid electrolyte, and a problem of damage remains in the case of using a solid electrolyte.
As described above, in the prior art, in actual use, the short circuit defect on the thin film liquid crystal substrate cannot be detected rapidly with high accuracy without causing damage to the substrate itself. Even if the pixel when the intersection between the scan line and the signal line and the thin film transistor itself are pluralized for each pixel, it cannot be specified at which intersection or at which thin film transistor the short circuit defect exists.